The invention relates to an exhaust-gas turbo-charger for an internal-combustion engine. More particularly the invention relates to an adjusting device for the throughput of exhaust gas through the turbine of an exhaust-gas turbocharger for an internal-combustion engine, the turbine having a doubleflow housing with two channels for supplying the exhaust gases to the turbine wheel, of which one channel can be closed off as a function of a variable operating parameter by means of a sliding sleeve which is mounted in the housing so as to be axially displaceable by means of slot-like longitudinal grooves in the manner of a positive sliding fit.
An exhaust-gas turbocharger of this type is known from German Patent Specification 2,633,587. In this known exhaust-gas turbocharger, the sliding sleeve is controlled via an annular piston which is fastened to it and which, on the one hand, is loaded by a spring and, on the other hand, can be subjected to the charging air. In such a control of the sliding sleeve, a clearly defined relationship between the position of the sliding sleeve and the regulating variable is not possible because of the varying frictional forces and changing spring forces, so that the one exhaust-gas channel cannot be closed off by the sliding sleeve in the desired way. At the same time, the spring loading the annular piston will change its spring characteristic rapidly, above all because of the high temperatures acting on it. The functioning of the large surface annular gasket of the annular piston is also put at risk, where its sealing effect is concerned, because of the high temperature load and the warping caused thereby, so that an indeterminate counterpressure can build up in the rear space of the annular piston.
An object on which the invention is based is to create an exhaust-gas turbocharger for an internal-combustion engine, having a sliding sleeve whose adjustment travel can be related to the regulating variable in a clearly defined manner, the control device remaining fully operative independently of the sealing, despite the high temperatures occurring in the region of the exhaust-gas turbocharger.
According to the invention, this object is achieved by providing an arrangement wherein the sliding sleeve is connected to an axially fixed and circumferentially rotatable driving ring via driving pins which engage into the longitudinal grooves arranged in the sliding sleeve and which drive these in the circumferential direction, wherein a slot pin fixed to the housing engages into a helical groove in the sliding sleeve, and wherein a shaft engages on the driving ring via positive connection and is guided radially out of the housing via a bearing in the latter.
In the exhaust-gas turbocharger designed according to preferred embodiments of the invention, the regulating variable acts on the shaft in the cool region outside the exhaust-gas turbocharger, the purely mechanical connection between the shaft and the sliding sleeve ensuring a clearly defined relationship between the regulating variable and the position of the sliding sleeve. The adjusting force to be exerted is determined solely by internal frictional forces, since the sliding sleeve is subjected to the same static pressure on all sides. At the same time, frictional forces cannot influence the accuracy of the adjustment travel of the sliding sleeve, and there is no need for a spring subject to temperature influences. The shaft is the only part which has to be sealed off at its exit from the turbocharger housing, but this is possible relatively easily because of the small diameter of the shaft and the fact that there is no axial displacement.
In especially preferred embodiments of the invention the bearing, consisting especially of ceramic, is designed as a labyrinth gasket, into which a sealing ring is additionally inserted. In these embodiments, the shaft mounting and shaft sealing are combined in a space saving way, the sealing effect being highly reliable as a result of labyrinth and sealing ring, but also because of the small dimensions of the sealing location. Furthermore, because of small angles of adjustment of the shaft without any axial displacement, the sealing ring is subjected to only little mechanical load.
According to especially preferred embodiments the positive connection is designed as a bevel wheel which is equipped with a toothing over some of its circumference and is fastened to the shaft and which engages into a bevel-wheel toothing formed laterally on the driving ring. As a result of this design, a space-saving, exact and temperature-resistant positive connection between the shaft and the driving ring is made.
An advantageous feature of certain preferred embodiments includes an arrangement wherein the driving ring is mounted on a housing ring inserted in the exhaust gas channel downstream of the turbine wheel and forming the channel wall, and pins inserted into the driving ring engage into an outer encircling groove in the housing ring. This arrangement provides not only the possibility of a separate assembly of the control device as a whole, but also protection of the moving parts from direct exposure to exhaust gases. Furthermore, a reliable axial fixing of the driving ring in the housing ring, with movability in the circumferential direction, is achieved.
According to certain preferred embodiments an arrangement is provided wherein the pins inserted into the driving ring and projecting outwards therefrom engage as said driving pins into longitudinal grooves of the sliding sleeve, thus forming the sliding fit. Within this arrangement a substantial simplification in terms of construction is obtained because the pins connecting the driving ring to the housing ring are used at the same time as driving pins for the sliding sleeve.
According to an advantageous feature of certain preferred embodiments the driving ring is mounted on the housing ring by means of ceramic balls. This ensures the further improvement in the guidance of the driving ring and a reduction of friction.
According to especially preferred embodiments an arrangement is provided wherein adjacent to that end region of the housing ring located on the same side as the turbine wheel and connected firmly to the housing ring by means of retaining pins, a contour ring is provided which is matched to the outer edges of the turbine wheel and on which the sliding sleeve is additionally mounted. This arrangement makes it easier not only to match the shape of the inner wall of the channel closely to the form of the turbine wheel, but also to assemble the control device and improve the guidance of the sliding sleeve.
According to certain preferred embodiments the contour ring forms the inner track shoulder for the bearing balls on the turbine wheel side. As a result of these features the contour ring is fixed exactly in relation to the driving ring, and the design of the ball-bearing is simplified.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.